One means for correcting or reducing understeer or oversteer slide in a vehicle is a torque-vectoring differential (TVD). TVD's are typically electronically-controlled differentials that are capable of creating a moment about the center of gravity of a vehicle independent of the speed of the vehicle wheels that would be employed to correct or reduce the understeer or oversteer slide.
U.S. Pat. No. 7,491,147 discloses an engine-driven TVD that employs a pair of speed control mechanisms that are disposed on opposite sides of a differential mechanism. Each speed control mechanism comprises a (spur) gear reduction and a friction clutch. The gear reduction transmits rotary power from a differential case of the differential mechanism to the friction clutch, and from the friction clutch to an associated (axle) output shaft.
Similarly, U.S. Pat. No. 7,238,140 discloses an engine-driven TVD that employs a pair of torque diverters that are disposed on opposite sides of a differential mechanism. Each torque diverter comprises a gear reduction and a magnetic particle brake. The gear reduction transmits rotary power from a differential case of the differential mechanism to an output member that is coupled to an associated axle output shaft for rotation therewith. The magnetic particle brake is configured to selectively brake the output member of the gear reduction.
U.S. Patent Application Publication No. 2010/0323837 discloses an electrically-driven TVD having a pair of planetary transmissions, an electric motor, and a sleeve that controls the operation of the planetary transmissions. The TVD can be operated in a first mode in which the TVD is configured as an open differential that is driven by the electric motor, and a second mode in which the TVD produces a torque vectoring output.
Other TVDs utilize two electric motors, with one motor being dedicated to driving an open differential and a second motor dedicated to providing torque vectoring to an output member of the open differential. Such a configuration can be complex and costly.
While such configurations can be effective for performing a torque vectoring function in which rotary power can be re-allocated across the differential mechanism from one axle shaft to the other, TVD's are nonetheless susceptible to improvement.